Field of the Invention
The present invention relates to a Group III nitride semiconductor light-emitting device, more specifically, a light-emitting device having a structure suitable for optical communication and having characteristics in light-emitting region.
Background Art
In short-distance optical fiber communication, POF (Plastic Optical Fiber) has been widely employed because it is inexpensive and resistant to bending. Since the POF exhibits low loss in a green band, Group III nitride semiconductor green light-emitting device is suitable as a light source for the POF. In such communication usage, the response speed of the light-emitting device is preferably fast. However, the response speed of the green light-emitting device is slow, and improvement is required.
A method of reducing the light-emitting area is known to improve the response speed of the light-emitting device (Patent Documents 1 to 3).
Patent Document 1 discloses a structure in which a p-pad electrode and a transparent electrode are formed apart from each other on a p-type layer, and a diffusion electrode is extended from the p-pad electrode to connect to the outer periphery of the transparent electrode. A region having the transparent electrode becomes an emission region by achieving better ohmic characteristics for the p-type layer in the transparent electrode than in the diffusion electrode.
Patent Documents 2 and 3 describe a flip-chip type Group III nitride semiconductor light-emitting device employed for optical communication. Patent Document 2 describes that an insulating film having a window is formed between the p-type layer and the reflection electrode, the current is interrupted in the region where the insulating film was formed, an electric conduction is obtained only in the window, thereby the window region becomes the emission region, and that the thickness of the insulating film is arranged to be one fourth of the wavelength of the emitted light, thereby improving the directivity of the optical axis direction. Patent Document 3 describes that the emission region is reduced by reducing an area of contact between an ohmic electrode and a p-type layer, thereby improving the response rate.
Patent Document 1: Japanese Patent Application Laid-Open (kokai) No. 2002-314130
Patent Document 2: Japanese Patent Application Laid-Open (kokai) No. 2003-347584
Patent Document 3: Japanese Patent Application Laid-Open (kokai) No. 2004-55855
However, there was a problem that the light output is reduced when the response speed is improved by reducing the light-emitting area.